Studies of mysid diets by gut contents analysis have generally revealed a broadly omnivorous feeding habit, but there are also tendencies towards carnivory, herbivory and/or detritivory (e.g. Nath & Pillai, 1973; Siegfried & Kopache, 1980; Mauchline, 1980; Zagursky & Feller, 1985; Wooldridge & Bailey, 1982; Webb & Wooldridge, 1989). Examination of feeding structures is also necessary to support inferences about feeding ecology (e.g. Webb & Wooldridge, 1989). However, there have been few studies relating to the functional morphology of mysid foreguts (Gelderd, 1909; Haffer, 1965; Nath & Pillai, 1973; Mauchline, 1980; Friesen et al., 1986; Webb & Wooldridge, 1989; Storch, 1989). With the exception of the latter two studies, qualitative descriptions and characterization of the different internal foregut structures have been primarily based on light microscopy. These studies may misinterpret the internal arrangement, topography, and three-dimensional orientation of the internal armature of the foregut, mainly due to problems with depth of field (Grice & Lawson, 1971). Oshel & Steele (1988), from SEM observations, briefly described some foregut features of Gnathophausia ingens. In a comparative study, Storch (1989), using the techniques of transmission and scanning electron microscopy, described in detail the different food chambers and channels, cuticular ridges, and ultrastructure of the epithelial and cuticular linings of the mysid foregut. Webb & Wooldridge (1989) noted the strong relationship between mouthparts, foregut morphology, and the feeding habits of two co-occurring mysids.